Process of crimping and setting textile strands



Aug- 17, 1 K. WVNICKI ETAL 3,200,467

PROCESS OF CRIMPING AND SETTING TEXTILE STRANDS Filed July 15, 1963 2 Sheets-Sheet 1 M %L%w W Attorneys 1955 K. lWNlCKl ETAL 3,200,467

PROCESS OF GRIMPING AND SETTING TEXTILE STRANDS Filed July 15, 1963 2 Sheets-Sheet 2 F/GZ.

Mwmi% v Attorneys United States Patent 3,269,467 PRQQESS 0F CRIMPKNG AND SETTING 'l'EXTilLE STRANDS Kurt lwniehi, Ponthir, and David ll. Miller, Stanmore, England, assignors to British Nylon Spinners Limited, lontypool, England ll iled July 15, 1963, Ser. No. 294,990 Qlaims priority, application Great Britain, July 19, 1962, 27,713/ 62 2 Claims. (Cl. 28-72) The invention concerns improvements in or relating to the crimping and setting of textile strands, and it has particular reference to such crimping and setting in a stufferbox.

As is now well-known in the textile art, crimping of textile strands so as to increase their bulltiness is frequently carried out. One process which has been employed for many years for crimping yarns, tows and slivers of both natural and man-made fibres or filaments is that of stuffer-box crimping, in which process the textile strand is forced into a confined space by driven nip rolls which form one boundary of said space, the emergence of the strand, in crimped form, from the other end of said space being yieldingly resisted by means imparting a back pressure to the mass of crimped strand within the space.

Depending on the uniformity of crimp which is required in the crimped strand, various measures may be taken to control the conditions of stutter-box crimping, so that, for instance, the crimp frequency may be maintained at a uniform value or the amount of crimped strand Within the stuffer-box may be maintained at a uniform value.

Setting of the crimped strand, as by the subjection thereof to heat with or without added moisture, may take place either whilst the strand is held confined within the stulferbox or after it has emerged therefrom. As in the matter of uniformity of crimp, so in the matter of uniformity of setting, various measures may be taken to control the conditions of setting to achieve the uniformity desired.

In the case of yarns and tows of synthetic thermoplastic materials such as the polyamides, polyesters and polyacrylonitriles, and also latterly the isotactic polypropylenes, both the uniformity of crimp and the uniformity of setting are of great importance, as any variations of either along a yarn or tow are likely to lead to visually observable streaks and other undesirable markings when the yarns or tows are further processed into knitting yarns, fabrics, or articles of clothing.

Having carried out considerable research into the desired rate of staffer-box crimping, particularly with respect to multifilament heavy denier yarns of polyhexamethylene adipamide, we have found that, for uniformity of both crimping and setting effects, it is of critical importance to control the back pressure, exerted on the crimped mass within the stuifer-box, at a position close to the nip rolls, and to carry out the setting treatment whilst the strand is held under pressure during a longer period than that for which the strand is under the controlled crimping pressure and, preferably, during such a longer period whose duration itself closely controlled.

These findings result essentially from the mutually contradictory nature of the requirements for uniform crimping and those for uniform and adequate setting.

Thus, it is not a satisfactory answer to set the crimped strand whilst it is under the crimping pressure, because then either the crimping pressure will be controlled through too long a column of crimped strand material for uniform crimping to be obtained, or the setting treatment Will not be applied for long enough for adequate effect even though severe conditions of setting, for instance of temperature, are employed.

Equally, however, it is no satisfactory answer to hold Bidddd? Patented Aug. 1'2, i965 the strand under crimping pressure for the minimum of space and time if a subsequent setting treatment is performed after the strands have been released from pressure altogether or if the duration of a setting treatment on a compacted mass of crimped strand is not uniformly controlled. Unless setting takes place whilst the crimped strand is held under pressure, some of the crimp imparted to the strand will be lost beforehand; and unless the duration of setting is maintained constant during the process, the resultant crimped and set strand will be likely to evince dyeing and other differences which may not be acceptable in the final textile product.

Lack of crimping uniformity when back pressure is controlled through too long a column of crimped strand material is thought to result from the facts that the crimped strand material does not behave as a fluid whilst in the stutter-box and that, in addition to uneven packing of the crimped strand material, the effects of friction of the walls of the stutter-box on the progress of the material through the box will assume greater significance the longer the column of material may be. Indeed, the frictional effects may vary as the duration of the crimping process increases, due in part to changes in the surface characteristics of the walls resulting from the temperature of working.

As a result of our findings, we have invented a process in which the conflicting requirements are largely reconoiled.

According to the invention, a process for crimping textile strands in a stutter-box crimper, in which process the strands are crimped and the crimp is set whilst the crimped strands are under pressure, is characterised in that the back pressure exerted on a strand at the successive instants of crimping is maintained constant by a continuous and automatic control of such pressure effective at a location intermediate of the point of crimping and the point of initiation of pressure on the strand within the stutter-box, and in that the crimp is set whilst the strand is under pressure within the stulfer-box.

Preferably, the rate or amount of withdrawal of the strand from the stutter-box is correlated with the rate or amount of feed, so that the amount of strand material within the stutter-box is maintained constant and hence the time during which the strand is undergoing the setting treatment is likewise kept constant. Such correlation may be achieved by a control of the rate or amount of feed, or by a control of the rate or amount of withdrawal, of the strand.

Setting may be effected by heat alone or by heat in combination with moisture. The duration of the setting treatment can be extended, compared with that normally employed, because of the divorcing of the pressure-controlling function from that of pressure initiation, which allows for the use of a long setting zone in the stutferbox in which zone the strand material is under pressure the whole time. As pointed out above, the fact of having a long column of strand material under pressure is not deleterious to good crimping so long as the pressure at the actual point of crimping is kept under constant control at a location near to that point, i.c. nearer to it than the point at which the pressure was initiated, which latter point will normally be at the point of discharge of the strand from the stuffenbox.

Owing to this extended duration of setting that is allowed by the invention, the conditions, such as those of temperature, do not have to be so severe as are sometimes required with existing staffer-box crimping processes. Less severe conditions, say a setting temperature of C. for heavy denier yarns of polyhexamethylene adipamide, when imposed over the allowable extended period of setting, will lead to thoroughly set crimp in the yarns. Shorter, more intensive, setting treatments are Wes) prone to be incompletely enective on the strand material in the middle of the stutter-box, as the outer portions of strand material act as heat insulators for the middle portion; or else the outer portions may even be damaged owing to excessive heat from the surfaces of the staffer-box in contact with them.

The presently preferred form of stutfenbox crimper for use in carrying out the invention is the subject of another patent application filed on even date hereto, and it will now be described with reference to the accompanying drawings, in which FIGURE 1 is a front elevational view of said crimper, shown partly in section where cut away; and FIGURE 2 is a side view, partly in section, of the apparatus of FIGURE 1.

In such crimper, the compression chamber is divided into a relatively short crimping zone and a relatively long setting Zone, and the end-portion of the chamber, comprising the setting Zone, is mounted for limited movement in its lengthwise direction relative to the other end-portion comprising the crimping zone.

The apparatus comprises nip rolls 1, 2 each of which is driven in the directions shown by the arrows in FIGURE 1. The drive is transmitted from endless bands 3, 4 (FIGURE 2) through pulley-wheels 5, 6 and gearbox 7. As shown in FIGURE 1, yarns Y converge at guide 9 before being led around a portion of the periphery of feed roll 11 pivotally mounted on arm 13 and held in contact with the periphery of nip roll 2 by means of weight 15 on the end of arm 13.

Nip rolls 1, 2 form the entry to the crimping zone endportion which is further bounded by front wall 17, back wall 19 and side walls 21, 22. Side walls 21, 22 have extensions 23, 24 at their lower ends which fit into the mouth of the setting zone end-portion, to be described below.

The setting zone end-portion consists of a rectangular cross section setting chamber 25 the main length of which is enclosed within a heater jacket 27. The end-portion is mounted on flexible steel spring cantilever arms 28, 29; and it is loaded, to be urged upwardly towards contact with the crimping zone end-portion, by means of weights 31 hung on the end of strand 33 passed around pulley wheel 35.

The discharge end of the chamber 25 is restricted by means of hinged flap 37 adjustably fixed in a desired position by means of screw 39. The front and back walls of the chamber are heated by electrical resistance heaters 41, 42, and the spaces 43, 44 within the jacket 27 may be filled with heat-insulating material.

The crimped yarn Y, is positively withdrawn from the setting chamber 25 around pin 45 by wind-up means (not shown).

The point of discharge from the setting zone is restricted so as to initiate the back pressure on the strand material within the compression chamber as a whole; and the actual pressure on the material within the crimping zone end-portion is controlled at a uniform value by reason of the load applied to the movable setting zone end-portion and tending to force said end-portion in the direction contrary to the direction of travel of the crimped strand through the crimper, which load is effective on the crimped strand material at the dividing line between the two end-portions. The limited movement of the setting zone end-portion can be utilised to activate means for varying the rate or amount of feed or the rate or amount of withdrawal of the strand to or from the crimper, so that the amount of strand within the crimper is maintained constant. Crimping pressure will be constant over limited movement of the setting zone end-portion since it is substantially independent, within the limits afforded by such movement, of the amount of yarn in the stutter-box. By employing such a floating setting zone end-portion, the control of pressure at the point of crimping, i.e. at the point where the strand is first discharged from the nip of the nip rolls, is effected at a location only a short distance from said point, being only separated therefrom by the length of the 4 crimping zone end-portion, which may be as little as an inch or two.

One way in which the amount of strand within the crimper can be maintained constant is by an electromechanical system, activated by movement of the setting zone end-portion, effective on the crimped strand after its withdrawal from the crimper to vary its tension. With such crimped strands, variations in tension can readily bring about the small increases or decreases in thickness of the strands that are all that is needed to vary the amount of strand material being withdrawn from the crimper, so as to keep the amount of material within it constant as crimping proceeds.

The initiation of back pressure by the restriction discharge end of the setting zone end-portion can very simply be effected by extending the front wall inwardly towards the back wall near to the point of discharge, instead of by the hinged flap. By reason of the preferential lay of the crimped strand within the compression chamber, only a small amount of restriction need be enforced in the width of the discharge end in the plane perpendicular to the plane of the nip rolls, to bring about the exertion of pressure backwardly along the mass of crimped strand material right to the point of crimping. The amount of restriction need not, in fact, amount to any restriction at all in crosssectional area of the discharge end of the setting zone compared with that of its input end, supposing that there is some divergence of the side walls of the setting zone end-portion.

The process of the invention has been proved to lead to uniformly crimped and uniformly crimp-set yarns of multifilamcnt polyhexamethylene adipamide. For instance, three such yarns of 1040 denier/ 68 filaments each have been crimped together in a stutter-box whose crimping zone was some 4 inches in length and fixedly mounted immediately above a movably mounted setting zone some 12 inches in length, the front and back walls of the setting zone end-portion being heated by electrical resistance heaters thereon to 180 C. when the yarns were forwarded to the crimper at a little under 1000 feet/minute and wound-up at 900 feet/minute. The movable setting zone end-portion was loaded with a weight of 9 lbs. to be forced upwardly towards contact with the discharge end of the crimping zone end-portion and to exert a backpressure of that load on the crimped yarns within the crimping chamber. The loading was simply achieved by hanging suflicient weights for counter-balancing and loading on a line passed around a pulley-wheel, the other end of the line being attached to a side of the setting zone endportion. Such end-portion was flexibly mounted for limited movement in the lengthwise direction on two cantilever arms of steel spring material. Any significant downward movement of the setting zone end-portion caused a microswitch to be made which energised a tensioning device acting on the crimped yarn bundle, so as to cause it to assume the lower tension setting of two settings. Conversely, when the end-portion was at its uppermost position, the tensioning device assumed the higher of its two settings, so as to remove less yarn from the crimper in unit time and allow the pressure to build up in the setting zone end-portion. The tension settings were determined empirically and they were such, being grams and 300 grams for the yarns concerned, to allow for a variation in thickness of the crimped yarn bundle of some 5%, which provides a close enough control of the amount of yarn within the crimper.

What we claim is:

1. In a process for crimping and setting textile strands in a stutter-box crimper while maintaining uniformity of crimping and setting effects, the steps comprising: forcing the strands from between nip rolls into a confined fixed compression chamber to subject them to back pressure for imparting crimp to them substantially at the point where the strands are discharged from the rolls; setting the crimp thus imparted to the strands by mainmo es? taining the crimped strands under pressure and passing them from the compression chamber to a setting chamber where heat is supplied to the strands; and continuously and automatically controlling the pressure in a manner to maintain the back pressure constant in the compression chamber and to hold the strands in the setting chamher under pressure during a longer period than that for which the strands are held in the compression chamber thereby maintaining uniformity of crimping and setting effects, said continuous and automatic control being effected by yieldingly urging the setting chamber in a direction opposite to the direction of travel of the strands through the chamber by applying a constant load to the setting chamber.

2. In a process for crimping and setting textile strands in a stutter-box crimper while maintaining uniformity of crimping and setting effects, the steps comprising: forcing the strands from between nip rolls into a confined fixed compression chamber to subject them to back pressure for imparting crimp to them substantially at the point where the strands are discharged from the rolls; setting the crimp thus imparted to the strands by maintaining the crimped strands under pressure and passing them from the compression chamber to a setting chamber Where heat is supplied to the strands; initiating said back pressure by yieldingly resisting emergence of the strands from the setting chamber; and continuously and automatically controlling the pressure which is effective at a location intermediate the point of crimping and the point of initiating the back pressure in a manner to maintain the back pressure constant in the compression chamber and to hold the strands in the setting chamber under pressure during a longer period than that for which the strands are held in the compression chamber thereby maintaining uniformity of crimping and setting efiects, said continuous and automatic control being etfected by yieldingly urging the setting chamber in a direction opposite to the direction of travel of the strands through the chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,865,080 12/58 Hentschel e 2872 3,009,310 11/61 Murchie et al. 28-72 3,023,481 3/62 Scragg 196 3,046,633 7/62 Ohashi et a1. 28-1 3,058,167 10/62 Rainard et al. 28--1 DONALD W. PARKER, Primary Examiner. 

1. IN A PROCESS FOR CRIMPING AND SETTING TEXTILE STRANDS IN A STUFFER-BOX CRIMPER WHILE MAINTAINING UNIFORMITY OF CRIMPING AND SETTING EFFECTS, THE STEPS COMPRISING: FORCING THE STRANDS FROM BETWEEN NIP ROLLS INTO A CONFINED FIXED COMPRESSION CHAMBER TO SUBJECT THEM TO BACK PRESSURE FOR IMPARTING CRIMP TO THEM SUBSTANTIALLY AT THE POINT WHERE THE STRANDS ARE DISCHARGED FROM THE ROLLS; SETTING THE CRIMP THUS IMPARTED TO THE STRANDS BY MAINTAINING THE CRIMPED STRANDS UNDER PRESSURE AND PASSING THEM FROM THE COMPRESSION CHAMBER TO A SETTIANG CHAMBER WHERE HEAT IS SUPPLIED TO THE STRNDS; AND CONTINUOUSLY AND AUTOMATICALLY CONTROLLING THE PRESSURE IN A MANNER TO MAINTAIN THE BACK PRESSURE CONSTANT IN THE COMPRESSION CHAMBER AND TO HOLD THE STRANDS IN THE SETTING CHAMBER UNDER PRESSURE DURING A LONGER PERIOD THAWN THAT FOR WHICH THE STRANDS ARE HELD IN THE COMPRESSION CHAMBER THEREBY MAINTAINING UNIFORMITY OF CRIMPING AND SETTING EFFECTS, SAID CONTINUOUS AND AUTOMATIC CONTROL BEING EFFECTED BY YIELDINGLY URGING THE SETTING CHAMBER IN DIRECTION OPPOSITE TO THE DIRECTION OF TRAVEL OF THE STRANDS THROUGH THE CHAMBER BY APPLYING A CONSTANT LOAD TO THE SETTING CHAMBER. 